net: dsa: microchip: ksz8: ksz8_fdb_dump: avoid extracting ghost entry from empty...

net: dsa: microchip: ksz8: ksz8_fdb_dump: avoid extracting ghost entry from empty dynamic MAC table.

[ Upstream commit 492606cdc74804d372ab1bdb8f3ef4a6fb6f9f59 ]

If the dynamic MAC table is empty, we will still extract one outdated
entry. Fix it by using correct bit offset.

Fixes: 4b20a07e103f ("net: dsa: microchip: ksz8795: add support for ksz88xx chips")
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Acked-by: Arun Ramadoss <arun.ramadoss@microchip.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>